The structure functions of the photon at large x

We derive 'improved' perturbative results in QCD for the structure functions of the photon at large Bjorken x by (a) using a correct phase-space treatment of the leading mass-singularity logarithms and (b) summing the leading logarithms of (1-x) associated with the wave function of the final state. We obtain explicit results in three kinematic regimes: (i) Q2 low enough for logarithmic QCD corrections to the parton model to be negligible; we estimate that this is the case for all presently realistic values of Q2(approx. <= 20 GeV2). (ii) Q2 high enough (at fixed x) for the effects of the leading mass-singularity logarithms to be important; we discuss the modifications to Witten's result at large x due to the correct kinematical treatment of the leading logarithms. (iii) Q2/s → infinite, where we sum the wave-function logarithms of (1-x); we show that F2sup(γ) → finite constant as Q2/s → infinite and that there is a close inclusive-exclusive connection in this limit. (orig.)